A known principle for extinguishing arcs in switch disconnectors and circuit breakers for alternating currents consists in forcing an arc with the aid of its own magnetic field into an extinction chamber provided specifically for this purpose, where it is split into a plurality of small arcs and cooled by the arrangement of extinction plates. This cooling causes a rise in voltage, which ultimately leads to the current being disconnected. The natural zero crossing of the current is also helpful here in the case of an applied alternating voltage source.
The extinction of arcs in the case of direct current switches is substantially more problematic in contrast since, especially in the case of high direct current voltages of up to 1500 volts, for example, and currents which are low relative to the nominal current (and which are dependent on the existing switch geometry), for example roughly 5 . . . 50 A, only a small magnetic field of the arc itself prevails, which is not normally sufficient to force the arc into an extinction chamber. A further problem is that no natural zero crossing exists in the case of direct currents, which makes the extinction of arcs even more difficult.
In an extreme case therefore when a direct current is switched, an arc between the open contacts of a switch can remain, not be extinguished and under certain circumstances destroy the switch, especially damage the switch contacts. Other standard protective devices such as circuit breakers likewise do not lead to the current being disconnected, since this is normally below the nominal current, i.e. there is an operating current for these protective devices which prevents disconnection.
EP 2 061 053 A2 discloses using the housing of a switching device for alternating current applications in the manufacture of a switching device for direct current applications and adapting this housing at low cost for direct current applications by adding a permanent magnet arranged in particular on the outside of the housing. As a result of this, the direct current switching capability of conventional alternating current switching devices is substantially increased since arcs are moved away from contact points of the switching device into extinction chambers by the permanent magnet field. It is also regarded as an advantage of the disclosure of EP 2 061 053 A2 that not every splitting surface and every extinction device needs to be assigned to one individual magnet each as is the case with known direct current switching devices.
W02012/076606A1 discloses a switch which is suitable for multipolar direct current operation independent of polarity and has at least two switching chambers. Each of the switching chambers has two extinction chambers with extinction plates to extinguish arcs occurring in the respective switching chamber between contact regions. Two magnets generate a magnetic field in the region of the switching contacts of all the switching chambers such that arcs are forced towards one of the extinction chambers of the switching chambers irrespective of the current direction in the arc. This switch exhibits rapid, reliable extinction behavior that is independent of the current direction and therefore prevents installation faults caused by polarity and is suitable for applications where switches are needed for both current directions.